In optical communications systems or networks, multiple optical signals may be transmitted and received at different channel wavelengths using wavelength division multiplexing (WDM) techniques. The optical communications system or network may include optical transceivers capable of transmitting and receiving optical signals at different channel wavelengths over a single optical fiber. An optical transceiver may include transmitter and receiver sub-assemblies and a WDM filter that separates the wavelength(s) being transmitted by the transmitter sub-assembly from the wavelength(s) being received by the receiver sub-assembly. In a passive optical network (PON), for example, an optical transceiver may transmit optical signals at wavelengths in the C-band and may receive optical signals at wavelengths in the L-band. Standard C-band and L-band optical transmissions, for example, are capable of providing optical signals on 32 different channels.
Some developing WDM-PON systems are designed to use more than the 32 channels used in standard C-band and L-band transmissions. The number of channels may be increased by reducing the unusable wavelengths between the C-band and L-band (e.g., <10 nm) and adding usable channel wavelengths. One way to decrease the unusable wavelengths is to decrease an angle of incident light on the WDM filter relative to a normal line. Reducing the incident light angle, however, may result in reflection back to the transceiver laser, which may adversely affect performance. Existing transceivers have used 45 degree WDM filters in an effort to reduce the incident angle while preventing unwanted back reflection; however, such transceivers may not sufficiently reduce the unusable wavelengths without significantly increasing the cost.